1. Field of the Invention
The present invention generally relates to vessel hulls and more specifically to a T-step hull form for mono-hull planing vessels.
2. Description of Related Art
Conventional stepped hulls are relatively well-known in the art of planing vessel hull forms and are useful in mono-hull designs (as compared to catamaran or trimaran designs). These hulls include one or more steps, or “breaks” in the hull, which are intended to reduce the amount of hull surface that comes in contact with the water. By reducing water contact, friction resistance is reduced leading to faster overall speed capability for a given vessel. Conventional stepped hull designs include a step that runs across the entire width (or “beam”) of the vessel, which step is usually located toward the back half of the hull. The step results in large apertures or gaps on the sides of the hull which provides ventilation for the hull.
These conventional stepped hull designs can result in a speed increase of about 10 to 15 percent for a given engine power output as compared to a non-stepped design. The speed increase occurs because the wetted area (i.e. the surface area of the hull that is in contact with water) is divided into smaller areas, each having a larger beam as compared to the length (i.e. larger aspect ratio). Lift generation is simply more efficient with a larger beam-to-length aspect ratio. Accordingly, with a stepped design, the hull can plane (i.e. achieve hydrodynamic lift) more efficiently on two or three high-aspect ratio surfaces rather than a single low-aspect ratio surface. In order for the increase in lift to occur over two or more high-aspect ratio surfaces, the rear of each step must be ventilated; this allows airs to be continuously sucked into the step region. Often, steps are ventilated to the outboard sides, at the transom, or both. Generally speaking, a stepped hull design allows for the adoption of lower output engine for a given set of desired performance characteristics, leading to an overall reduction in cost of the vessel and an increase in fuel efficiency. To that end, the cost of engines is often the largest single cost in recreational vessels and therefore if smaller engines can be used while still meeting desired performance expectations, a significant advantage can be gained.
Despite the speed benefits, conventional stepped hull designs are known to reduce stability, particularly at high speeds. This is because lift is spread laterally across more than one surface, which increases longitudinal stability, making it more difficult to trim the vessel. Without proper trimming, conventional stepped hull vessels can tend to swap ends and/or broach, i.e. become air-borne, while maneuvering. Stability can be achieved through the effective use of trim tabs (i.e. adjustable flaps fitted to the hull at the transom which correct/change the center of gravity of the vessel), but properly adjusting the tabs “on the fly” requires a boater with advanced knowledge and experience. Consequently, high speed maneuvering of stepped hull vessels can be quite dangerous, particularly for less-experiences boaters who are not proficient in setting the trim of the vessel. Further still, conventional stepped hull designs suffer from increased drag at low speeds, before higher speeds cause water to break cleanly off the step
Several attempts at providing stepped hull designs are relatively well-known in the art; however, none are specifically designed to improve handling and stability characteristics, particularly during high speed maneuvering:
For example, U.S. Pat. No. 1,832,862 to Grumman relates to a hull design for a seaplane or amphibian aircraft designed to reduce suction of the water during takeoff. The hull includes a stepped rearward section having a diminutive keel running the length of the hull. The design provides for an upwardly sloped rearward section to keep the surface clear of the water leaving the step. A triangular flat bottom section is located at the apex of the bend of the keel, at the step, and facilitates early take off from a body of water.
U.S. Pat. No. 5,111,767 to Haines describes a boat hull having a flat, recessed section intersecting the transom along with a vent means and drain for ventilating an internal hollow body or reservoir mounted within the hull. The recessed section extends only partially along the beam of the hull, on either side of the centerline (keel) thereof and vents only rearward to the transom. The keel of the hull is completely interrupted at the recess. The venting body and recess prevents water from gaining access to the hull interior, trapping and expelling such water through the transom.
U.S. Pat. No. 5,191,853 to Adler describes a stepped hydroplane hull wherein the aft section has a positive trim angle and a forward portion has either a flat or positive trim angle wherein the angle of the forward portion is less than that of the aft portion. The hull also includes a region immediately aft of the step which is ventilated to atmosphere by air passages joining the step above the water line, in order to reduce drag at pre-planing speeds when the step is completely immersed in water. The air passages are not longitudinally placed and ventilation actually occurs through the hull. As with traditional stepped hull designs, the keel of the hull is stepped as well, decreasing handling stability at high speeds.
Japanese Patent No. JP6-227478 to Yamashita describes a hull design having a forward stepped section, a longitudinally oriented keel, a transverse hydrofoil, and catamaran-like side hulls. The hull results in a main center hull stabilized by smaller demihulls with a hydrofoil connecting the demihulls, with the hydrofoil generating planing lift.
Russian Patent No. RU2161105 describes a high speed ship hull having a stepped recess in an internal section of the hull, and substantially flanged sidewalls. The forward portion of the hull has one or more air distributor holes. The stepped section does not extend to the chines of the hull and thus the hull does not ventilate at the sides of the vessel. Further, the keel is stepped along with the stepped section, limiting high speed handling stability.
Consequently, there is a marked need for a stepped hull design that provides increased speed characteristics and efficiency benefits as compared to traditional mono-hull designs, while also providing greatly improved stability and handling characteristics as compared to known stepped hull designs. It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed. However, in view of the heat exchanger systems in existence at the time of the present invention, it was not obvious to those persons of ordinary skill in the pertinent art as to how the identified needs could be fulfilled in an advantageous manner.